These are two implementations of MPI (Message Passing Interface).
See http://www.mcs.anl.gov/mpi/index.html for further details.

mpinu.tar.gz:
  The first implementation grew out of an independent study in Fall, 1996
  with an undergraduate student who wishes to remain nameless,  At that time,
  we tried to maintain compatibility with both K&R C and ANSI C,
  while today, ANSI C alone would suffice.  The software was then
  partially rewritten by me, so as to provide a small subset implementation
  of MPI with a small footprint, sufficient to include in some of my
  other distributions:  TOP-C, ParGAP/MPI, etc.
  I take full responsibility for any remaining bugs.

mpinu2.tar.gz:
  The second implementation was written by a graduate student, Predrag
  Petkovic (predrag@ccs.neu.edu) in Fall, 1999 as a course project.  I
  provided the initial specifications, the MPI home page, the earlier
  implementation of mpinu, and only a very small amount of discussion,
  The student then did a very professional job of implementing most of the
  layers of MPI (however not topology, for example), and went on to implement
  the Spawn() command as specified by MPI-2.